东昆仑诺木洪地区新元古代眼球状花岗片麻岩锆石U-Pb年龄及Hf同位素特征

Zircon U-Pb age and Hf isotopic characteristics of the Neoproterozoic globular granitic gneiss in Nomuhong area,east Kunlun

对东昆仑诺木洪地区白沙河岩组眼球状花岗片麻岩中。锆石进行U-Pb测年结果表明,该片麻岩可能形成于921 Ma左右,其中含有的残留锆石核反映其可能来自于中元古代地壳物质的再循环;对锆石Hf同位素测定结果显示其具有正的εHf(t),且位于1100~1500 Ma的平均地壳演化线之间,同样暗示其来自于中元古代古老地壳物质。结合区域上存在同时期的双峰式侵入岩,推测该眼球状花岗片麻岩形成于伸展环境下,地幔上涌引起上覆中元古代的白沙河岩组为代表的表壳岩系发生熔融,并侵入其中,之后再共同经历了后期的角闪岩相变质。

Zircon U-Pb geochronology and zircon Hf isotope study were carried out on the spheroidal granitic gneiss in the Baishahe Formation of the Nomuhong area in east Kunlun. The zircon U-Pb dating results indicate that the gneiss may be formed at around 921 Ma,and the residual zircon core contained therein may reflect the recirculation of the Mesoproterozoic crustal material. The zircon Hf isotope results show that it has a positive εHf(t) and lies between the average crust evolution lines of 1100 ~ 1500 Ma,which also implies that it originated from the Middle Proterozoic ancient crustal material. There are contemporaneous bimodal intrusive rocks in the combined area. It is speculated that the globular granitic gneiss may be formed in the extended environment,and the mantle upwell caused the overlying metamorphic Paleozoic Baishahe Formation as the representative case rock series. Melting occurs and invades it,and then undergoes a later amphibolite facies metamorphism.